This invention relates to the field of machine vision, and more specifically to a method and precision apparatus of obtaining three-dimensional inspection data for manufactured parts in a manufacturing environment.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings hereto: Copyright(copyright) 1998-2000, PPT Vision, Inc., All Rights Reserved.
There is a widespread need for inspection data for electronic parts in a manufacturing environment. One common inspection method uses a video camera to acquire two-dimensional images of a device-under-test.
Height distribution of a surface can be obtained by projecting a light-stripe pattern onto the surface and then re-imaging the light pattern that appears on the surface.
One technique for extracting this information based on taking multiple images (3 or more) of the light pattern that appears on the surface while shifting the position (phase) of the projected light stripe pattern is referred to as phase shifting interferometry, as disclosed in U.S. Pat. Nos. 4,641,972 and 4,212,073 (incorporated herein by reference).
The multiple images are usually taken using a CCD (charge-coupled device) video camera with the images being digitized and transferred to a computer where phase-shift analysis, based on images being used as xe2x80x9cbuckets,xe2x80x9d converts the information to a contour map (i.e., a three-dimensional representation) of the surface.
The techniques used to obtain the multiple images are based on methods that keep the camera and viewed surface stationary with respect to each other while moving the projected pattern.
One technique for capturing just one bucket image using a line scan camera is described in U.S. Pat. No. 4,965,665 (incorporated herein by reference).
U.S. Pat. No. 5,398,113 and 5,355,221 (incorporated herein by reference) disclose white-light interferometry systems which profile surfaces of objects.
In U.S. Pat. No. 5,636,025 (incorporated herein by reference), an optical measuring system is disclosed which includes a light source, gratings, lenses, and camera. A mechanical translation device moves one of the gratings in a plane parallel to a reference surface to effect a phase shift of a projected image of the grating on the contoured surface to be measured. A second mechanical translation device moves one of the lenses to effect a change in the contour interval. A first phase of the points on the contoured surface is taken, via a four-bucket algorithm, at a first contour interval. A second phase of the points is taken at a second contour interval. A control system, including a computer, determines a coarse measurement using the difference between the first and second phases. The control system further determines a fine measurement using either the first or second phase. The displacement or distance, relative to the reference plane, of each point is determined, via the control system, using the fine and coarse measurements.
Current vision inspection systems have many problems. Among the problems are assorted problems associated with the mechanical translation devices used with the vision inspection systems to handle the devices under inspection. One problem is that vision systems typically take up a large amount of linear space on a manufacturing line. Typically small devices, such as disk-drive suspensions, are placed in standard trays, to facilitate the handling of the small devices. In other cases, the disk-drive suspensions are manufactured from a continuous strip of thin metal, wherein at least a portion of the strip is maintained, with other portions cut away to form the suspensions, thus leaving the suspensions attached to the remaining strip. The suspensions can bend at various angles relative to the strip they are attached to. This strip is then used to facilitate the handling of the suspensions, such as positioning the suspensions under a machine-vision head at an inspection station. The exact positioning of the suspensions in their trays, or their relative orientation to the strip can vary, putting demands on the machine-vision system to determine the orientation and angle of the parts relative to the machine-vision head.
Conventional 3D imaging systems and methods have difficulty in obtaining both speed and accuracy. The support and motion control of the scanning head relative to the parts being scanned present substantial challenges. In particular, vibration problems as well as difficulty in maintaining tight tolerances of scan height across the length of the scan motion make it difficult to obtain accurate measurements of very small parts or parts having a requirement for extreme precision in 3 dimensional geometric measurements.
To overcome the problems stated above as well as other problems, there is a need for a method and precision apparatus of obtaining three-dimensional inspection data for manufactured parts in a manufacturing environment.
In the context of a machine-vision system for inspecting a part, this invention includes method and apparatus to provide high-speed 3D (three-dimensional) inspection of manufactured parts. In some embodiments, precision stamped, formed, and/or laser-cut metal parts are inspected to obtain dimensional and geometric information regarding such characteristics as sag or bow of subportions of the item, the angle of pitch, yaw, and or roll of one portion relative to another, heights of various formations on the part. In some embodiments, this invention includes method and apparatus to provide high-speed 3D inspection of manufactured parts.
One aspect of the present invention provides a machine-vision system for inspecting an object. The system includes a machine-base unit and a table-base portion supported by the base unit. At least two upright portions are connected to the table-base portion. A first scanner support is coupled to the upright portions. An imager head is coupled to the scanner support, wherein the scanner support moves the imager head in a linear motion to scan the object. A connecting member including at least one vibration-absorbing portion connects to the upright portions to absorb vibrations of the upright portions.
Another aspect of the present invention provides a method of reducing vibration in a three-dimensional scanning apparatus used to determine a geometry of an object having at least one surface to be measured, the scanning apparatus having two or more upright portions and a scanning mechanism coupled the upright portions for moving an imaging head. The method includes supporting the scanning mechanism on the upright portions, dampening vibrations of the upright portions, scanning the imaging head relative to the object, receiving image signals representing a three-dimensional geometry of the object into a computer, and calculating with the computer object-geometry data representing three-dimensional geometry of the object.